Studies on Calibration of Medical Carbon Dioxide Incubator

Han Luo

1a

, Tingting Ren

2b

, Yang Xu

1c

, Zhongmu Zhou

1d

and Huijuan Wang

1e

1

Center for Medical Metrology, Chongqing Academy of Metrology and Quality Inspection, Chongqing, China

2

Center for Length Metrology, Chongqing Academy of Metrology and Quality Inspection, Chongqing, China

Keywords: Medical Carbon Dioxide Incubator, Calibration, Temperature Deviation, Temperature Fluctuation,

Temperature Uniformity, CO

2

Concentration Indication Error, CO

2

Concentration Control Error, Humidity.

Abstract: Medical carbon dioxide incubator is widely used in medical microbiological and biotechnological laboratories

to simulate the growth environment for in vitro culture of cells or tissues of organisms. This article presents

a novel design of calibration procedure to test the essential parameters of the medical carbon dioxide incubator

such as "temperature deviation", "temperature fluctuation", "temperature uniformity", "CO2 concentration

indication error", "CO2 concentration control error" and "humidity" in order to ensure the accuracy and

reliability of the instrument. The research result can ensure the metrological traceability of medical carbon

dioxide incubator by studying the instrument’s key technical parameters and selecting the suitable

metrological standards.

1 INTRODUCTION

Medical carbon dioxide incubator is widely used in

medical microbiological and biotechnological

laboratories to simulate the growth environment for

in vitro culture of cells or tissues of organisms.

Usually, the temperature inside the chamber is

regulated at 37℃, and the CO

2

content of the

atmosphere in the chamber is regulated at 5%. The

main difference between medical carbon dioxide

incubator and normal incubator is that the former can

provide a certain concentration of CO

2

in order to

meet the growth environment requirements of

microorganism. Medical carbon dioxide incubator is

essential metrological equipment for cell, tissue and

bacterial culture in immunology, oncology, genetics

and bioengineering researches. However, till now,

national metrological verification regulation has not

been issued applicable to the calibration of medical

carbon dioxide incubator, therefore, and the

corresponding traceability system of which has not

been established yet.

The purpose of this paper is to study the

influencing factors on essential technical parameter

such as "temperature deviation", "temperature

a

https://orcid.org/0000-0003-0763-3727

b

https://orcid.org/0000-0002-6320-0179

c

https://orcid.org/0000-0001-8385-9790

fluctuation", "temperature uniformity", "CO

2

concentration indication error", " CO

2

concentration

control error" and "humidity" of medical carbon

dioxide incubator, as well as to determine the

measuring standards and to establish an applicable

calibration procedure, in order to improve research

conditions of medical laboratories, and furthermore,

to establish the traceability system of medical carbon

dioxide incubator.

2 CLIBRATION CONDITIONS

2.1 Environmental Conditions

Temperature: (15~35) ℃;

Humidity: ≤85%RH;

The environmental conditions shall also meet the

requirements for the normal use of measuring

standards and other supporting equipment.

d

https://orcid.org/0000-0002-9082-4681

e

https://orcid.org/0000-0001-6633-6453

Luo, H., Ren, T., Xu, Y., Zhou, Z. and Wang, H.

Studies on Calibration of Medical Carbon Dioxide Incubator.

DOI: 10.5220/0011186700003444

In Proceedings of the 2nd Conference on Artiﬁcial Intelligence and Healthcare (CAIH 2021), pages 91-96

ISBN: 978-989-758-594-4

Copyright

c

91

2.2 Measuring Standards and Other

Supporting Equipment

Table 1: Measuring Standards and Other Supporting

Equipment.

Measuring

Range

Technical

Requirements

Standard

Thermomete

r

(0~65) ℃

Definition: ≤0.1℃

MPE: ±0.2℃

Standard CO

2

Senso

r

(0~20)%

Definition: ≤0.1%

MPE: ±0.3%

Standard

Humidity

Senso

r

(10~100)%RH

Definition: ≤0.1%

MPE: ±2.0%RH

3 TEMPERATURE CLIBRATION

3.1 Temperature Calibration

Procedure and Calculation

Equations

Place 9 calibrated standard thermometers in the

empty chamber of medical carbon dioxide with

shelves in place as demonstrated in Figure 1. Locate

standard thermometers (marked as 1, 2, 3, 4, 5, 6, 7,

8) in each of the eight corners of the incubator

approximately 1/10 length of the side from each wall,

and place the ninth standard thermometer (marked as

9) in the geometric center of the chamber.

Figure1: Positioning of Standard Sensors

Set the control temperature at 37°C. Take 16

readings of each standard thermometer as well as the

incubator’s temperature indication value at regular

intervals of 2min in 30 min during steady temperature

condition. Calculate the temperature deviation,

temperature fluctuation and uniformity according to

equation (1), (2), (3):

0

ttt

d

−=Δ

(1)

tΔ

—Temperature deviation, ℃;

d

t

—Average indication temperature of medical

carbon dioxide incubator, ℃;

0

t

—The average temperature measured by

standard thermometer 9 located in the geometric

center, ℃.

2/)(

min0max0

ttt

f

−±=Δ

(2)

f

t

Δ

—Temperature fluctuation, ℃;

max0

t

—The maximum temperature value

measured by standard thermometer 9 located in the

geometric center, ℃;

min0

t

—The minimum temperature value measured

by standard thermometers located in the geometric

center, ℃.

2/)(

minmax

ttt

u

−=Δ

(3)

max

t

—The maximum temperature reading taken

by standard thermometers during 30min, ℃;

mini

t

—The minimum temperature reading taken

by standard thermometers during 30min, ℃;

u

tΔ

—Temperature uniformity, ℃.

3.2 Experimental Results of

Temperature Calibration

Select several typical types of medical carbon dioxide

incubators as the calibrated subjects. The

experimental result is demonstrated in Table 2.

Table 2: Temperature Calibration Results (unit:℃).

Type Deviation Fluctuation Uniformity

3111 0.2 ±0.05 0.5

3131 0.2 ±0.05 0.4

371 0.2 ±0.1 0.5

HF240 -0.3 ±0.1 0.4

HF240 0.3 ±0.1 0.5

HF151 -0.2 ±0.2 0.3

HF90 -0.3 ±0.2 0.4

WJ-3-160 0.2 ±0.05 0.3

The temperature deviation and fluctuation

calibration results have met the metrological criterion

set by YY 1621-2018 Medical carbon dioxide

incubator of no more than ±0.3 ℃. The temperature

uniformity calibration results have met the

metrological criterion set by YY 1621-2018 Medical

carbon dioxide incubator of no more than ±0.5 ℃.

4 CO

2

CONCENTRATION CALI-

BRATION

4.1 CO

2

Concentration Calibration

Procedure and Calculation

Equations

Place the standard CO

2

Senor (marked as O) in the

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geometric center of the incubator chamber as

demonstrated in Figure 1.

Set the incubator’s control temperature at 37°C

and the CO

2

concentration value at 5%. Take 10

readings of the standard CO

2

sensor as well as the

incubator’s CO

2

concentration indication value at

regular intervals of 15min 2 hours after the set value

of temperature and CO

2

concentration has reached.

Calculate the CO

2

concentration indication error and

control error according to equation (4), (5):

sdd

CCC −=

(4)

d

C

—CO

2

concentration indication error, %;

d

C

—Average value of 10 CO

2

concentration

indication readings of the incubator, %;

s

C

—CO

2

concentration set value of incubator, %.

sc

CCC −=

(5)

c

C

—CO

2

concentration control error, %;

C

—Average value of 10 readings of CO

2

sensor,

%.

4.2 Experimental Results of CO

2

Concentration Calibration

Select several typical types of medical carbon dioxide

incubators as the calibrated subjects. The

experimental result is demonstrated in Table 3:

Table 3: CO

2

Concentration Calibration Results (unit: %).

Type Indication Erro

r

Control Erro

r

3111 0.1 0.3

3131 -0.2 -0.4

371 0.2 0.4

HF240 0.1 0.2

HF240 0.1 0.1

HF151 0.2 -0.4

HF90 -0.1 -0.2

WJ-3-160 0.1 0.1

The CO

2

concentration indication error

calibration results have met the metrological

criterion set by YY 1621-2018 Medical carbon

dioxide incubator of no more than ±0.2%, and the

CO

2

concentration control error calibration results

have met the metrological criterion set by YY 1621-

2018 Medical carbon dioxide incubator of no more

than ±0.5%.

5 HUMIDITY CALIBRATION

5.1 Humidity Calibration Procedure

Place the standard humidity

Senor (marked as O) in

the geometric center of the incubator chamber as

demonstrated in Figure 1.

Set the incubator’s control temperature at 37°C

and the CO

2

concentration value at 0%. Take the

reading of the standard humidity

sensor 2 hours after

the set value of temperature.

5.2 Experimental Results of Humidity

Calibration

Select several typical types of medical carbon dioxide

incubators as the calibrated subjects. The

experimental result is demonstrated in Table 4.

Table 4: Humidity Calibration Results (unit: %).

Type

Humidity measured by Standard

Senso

r

3111 97.6

3131 98.1

371 99.0

HF240 97.9

HF240 98.2

HF151 99.1

HF90 99.0

WJ-3-160 99.5

The humidity calibration results have met the

metrological criterion set by enterprise standards of

no less than 95%.

6 UNCERTAINTY ANALYSIS

6.1 Uncertainty Analysis on

Temperature Measurement

6.1.1 Standard Uncertainty Introduced by

Temperature Measurement

Repeatability

Select a type 3111 medical carbon dioxide incubator

to conduct the temperature calibration procedure

presented in Chapter 3 at the set value of 37℃. The

obtained values are demonstrated in Table 5:

Table 5: Temperature Repeatability Test Result (unit: ℃).

No. Measured Temperature

1 36.8

2 36.9

3 36.8

4 36.7

5

36.8

6

36.7

7 36.9

8

36.8

Studies on Calibration of Medical Carbon Dioxide Incubator

93

9

36.8

10

36.7

Sum

367.9

___

t

36.79

Calculates the standard deviation with Bessel

formula:

℃074.0

110

)(

1

)(

10

1

2

___

1

2

=

−

=

−

=



=− i

i

n

i

tt

n

tt

ts

(6)

16 readings shall be taken when the medical

carbon dioxide incubator is calibrated in practical

use. So the standard uncertainty introduced by

measurement repeatability is as follows:

℃

0185.0

16

)(

1

==

t

s

u

(7)

6.1.2 Standard Uncertainty Introduced by

the Resolution of Standard

Thermometer

The resolution of standard thermometer is 0.1℃,

considering uniform distribution, the standard

uncertainty introduced by the resolution is as follows:

℃

029.0

32

1.0

2

==u

(8)

6.1.3 Standard Uncertainty Introduced by

the Maximum Permissive Error of

Standard Thermometer

The maximum permissive error of standard

thermometer is ±0.2℃, considering uniform

distribution, the standard uncertainty introduced by

maximum permissive error is as follows:

℃

05.0

32

2.0

3

==u

(9)

6.1.4 Synthetic Uncertainty of Temperature

Measurement

The uncertainty components analyzed are shown in

Table 6:

Table 6: Summary of Uncertainty Components of

Temperature Measurement (Unit: ℃).

Source of Standard

Uncertaint

y

Uncertainty

T

yp

e

Uncertainty

Measurement

Repeatabilit

y

A 0.0185

Resolution of

Standard

Thermomete

r

B 0.029

The Maximum

Permissive Error of

Standard

Thermomete

r

B 0.058

Since the standard uncertainty introduced by the

resolution of standard thermometer

℃

029.0

2

=u

is

positively correlated with the uncertainty introduced

by measurement repeatability

℃

0.0185

1

=u

,

therefore, only the standard uncertainty introduced by

resolution of standard thermometer

2

u

is considered,

when synthetic uncertainty is calculated as follows:

℃

064.0

32c

=+= uuu

(10)

6.1.5 Extended Uncertainty of Temperature

Measurement

Take the inclusion factor k=2 (confidence probability

is 95%), the extended uncertainty is calculated as

follows:

℃0.130.12820.064

c

≈=×== kuU

(11)

6.2 Uncertainty Analysis on CO

2

Concentration Measurement

6.2.1 Standard Uncertainty Introduced by

CO

2

Concentration Measurement

Repeatability

Select a type 3111 medical carbon dioxide incubator

to conduct the CO

2

concentration calibration

procedure presented in Chapter 4 at the set value of

5%. The obtained values are demonstrated in Table 7:

Table 7: CO

2

Concentration Repeatability Test Result.

No. Measured CO

2

Concentration/%

1 4.8

2 4.7

3 4.8

4 4.7

5 4.9

6 4.6

7 4.7

8 4.8

9 4.8

10 4.7

Sum 47.5

___

t

4.75

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Calculates the standard deviation with Bessel

formula:

%085.0

110

)(

1

)(

10

1

2

___

1

2

=

−

=

−

=



=− i

i

n

i

tt

n

tt

ts

(12)

10 readings shall be taken when the medical

carbon dioxide incubator is calibrated in practical

use. So the standard uncertainty introduced by

measurement repeatability is as follows:

%027.0

10

)(

1

==

t

s

u

(13)

6.2.2 Standard Uncertainty Introduced by

the Resolution of Standard CO

2

Sensor

The resolution of standard CO

2

sensor is 0.1%,

considering uniform distribution, the standard

uncertainty introduced by the resolution is as follows:

%029.0

32

1.0

2

==u

(14)

6.2.3 Standard Uncertainty Introduced by

the Maximum Permissive Error of

Standard CO

2

Sensor

The maximum permissive error of standard CO

2

sensor is ±0.3%, considering uniform distribution, the

standard uncertainty introduced by maximum

permissive error is as follows:

87%0.0

32

3.0

3

==u

(15)

6.2.4 Synthetic Uncertainty of CO

2

Concentration Measurement

The uncertainty components analyzed are shown in

Table 8:

Table 8: Summary of Uncertainty Components of CO

2

Concentration Measurement.

Source of Standard

Uncertainty

Type

Uncertainty

(%)

Measurement Repeatability A 0.31

Resolution of Humidity

Senso

r

B 0.029

The Maximum Permissive

Error of Humidity

Senso

r

B 0.58

Since the standard uncertainty introduced by the

resolution of standard CO

2

sensor

%029.0

2

=u

is

positively correlated with the uncertainty introduced

by measurement repeatability

7%02.0

1

=u

, therefore,

only the standard uncertainty introduced by

resolution of standard CO

2

sensor

2

u

is considered,

when synthetic uncertainty is calculated as follows:

0.092%

32c

=+= uuu

(16)

6.2.5 Extended Uncertainty of CO

2

Concentration Measurement

Take the inclusion factor k=2 (confidence probability

is 95%), the extended uncertainty is calculated as

follows:

℃

0.20.18420.092

c

≈=×== kuU

(17)

6.3 Uncertainty Analysis on Humidity

Measurement

6.3.1 Standard Uncertainty Introduced by

Humidity Measurement Repeatability

Select a type 3111 medical carbon dioxide incubator

to conduct the humidity calibration procedure

presented in Chapter 5. The obtained values are

demonstrated in Table 9:

Table 9: Humidity Repeatability Test Result.

No.

Humidity measured by Standard Sensor

/%

1 97.8

2 97.9

3 98.0

4 98.2

5 97.6

6 97.9

7 97.7

8 98.5

9 97.5

10 97.6

Sum 978.7

___

t

97.87

Calculates the standard deviation with Bessel

formula:

31%.0

110

)(

1

)(

10

1

2

___

1

2

=

−

=

−

=



=− i

i

n

i

tt

n

tt

ts

( 1 8 )

6.3.2 Standard Uncertainty Introduced by

the Resolution of Standard Humidity

Sensor

The resolution of standard humidity

sensor is 0.1%,

considering uniform distribution, the standard

Studies on Calibration of Medical Carbon Dioxide Incubator

95

uncertainty introduced by the resolution is as follows:

%029.0

32

1.0

2

==u

(19)

6.3.3 Standard Uncertainty Introduced by

the Maximum Permissive Error of

Standard Humidity Sensor

The maximum permissive error of standard humidity

sensor is ±2.0%, considering uniform distribution, the

standard uncertainty introduced by maximum

permissive error is as follows:

58%.0

32

2

3

==u

(20)

6.3.4 Synthetic Uncertainty of Humidity

Measurement

The uncertainty components analyzed are shown in

Table 10:

Table 10: Summary of Uncertainty Components of CO

2

Concentration Measurement.

Source of Standard

Uncertaint

y

Uncertainty

Type

Uncertainty

(%)

Measurement

Re

p

eatabilit

y

A 0.027

Resolution of Standard

CO

2

Senso

r

B 0.029

The Maximum

Permissive Error of

CO

2

Senso

r

B 0.087

Since the standard uncertainty introduced by the

resolution of standard humidity

sensor

%029.0

2

=u

is

positively correlated with the uncertainty introduced

by measurement repeatability

0.31%

1

=u

, therefore,

only the standard uncertainty introduced by

measurement repeatability

1

u

is considered, when

synthetic uncertainty is calculated as follows:

0.66%

31c

=+= uuu

(21)

6.3.5 Extended Uncertainty of Humidity

Measurement

Take the inclusion factor k=2 (confidence probability

is 95%), the extended uncertainty is calculated as

follows:

1.3%1.3220.66

c

≈=×== kuU

(22)

7 CONCLUSION

The article studies the key technical parameters such

as "temperature deviation", "temperature

fluctuation", "temperature uniformity", "CO

2

concentration indication error", " CO

2

concentration

control error" of medical carbon dioxide incubator,

determines the appropriate standards and supporting

instruments for measuring, and performs the novel

calibration procedure presented in this article on

several typical types of medical carbon dioxide

incubators widely used in China. The testing results

meet the requirements of national standard YY1621-

2018.

Therefore, the article presents a feasible

procedure for the periodic calibration of medical

carbon dioxide incubator in order to establish the

metrological traceability system of the instrument.

Further work is worth to be done to improve the

calibration method of medical carbon dioxide

incubator.

ACKNOWLEDGEMENTS

Our work was supported by National Metrology

Verification Regulation Program of China (Grant No.

MTC-2019-163).

REFERENCES

ASTM E1292 (2011) Standard Specification for Gravity

Convection and Forced Ventilation Incubators.

American Society of Testing Materials, West

Conshohoken.

JJF 1101(2019)

Calibration Specification of Environmental

Testing Equipment for Temperature and Humidity

Parameters. State General Administration for Quality

Supervision and Inspection and Quarantine, Beijing.

YY 1621(2018)

Medical carbon dioxide incubator.

National Medical Products Administration, Beijing.

ZHOU A.S., et al.. Evaluation of Uncertainty in

Measurement of CO

2

Incubators[J]. Metrology &

Measurement Techniques, 2011.38(11):55-56

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